Impact of Completion Design on Fracture Complexity in Horizontal Shale Wells

A proppant-filled fracture induces mechanical stresses in the surrounding rock that cause a reduction in the horizontal-stress contrast and stress reorientation around the open fracture. A 3D geomechanical model is used to simulate the stress reorientation caused by open fractures and to generate horizontal-stress-contrast contour maps. The reduction in horizontal-stress contrast can lead to increased fracture complexity. This paper describes ways to increase fracture complexity by varying the completion design. In this paper, we identify the impact of operator-controllable variables in a completion design on fracture complexity. This can lead to more-effective completion designs that improve well productivity, reservoir drainage, and, ultimately, the estimated ultimate recovery (EUR). The possibility of greater fracture complexity and reduced/effective fracture spacing and, thus, a higher drainage area is demonstrated for the alternate fracturing sequence in comparison to the conventional fracturing sequence. The Young's-modulus value of the shale and the in-situ horizontal-stress contrast are shown to be significant factors controlling the extent of fracture complexity generated in a given reservoir. In addition, the effect of proppant mass injected per stage is also shown to significantly impact fracture complexity. We provide optimal ranges of fracture spacing and proppant volume for the various shale formations analyzed. The use of these guidelines should result in more fracture complexity than would otherwise be observed. The results presented in the paper provide the operator with the knowledge to design completions and fracture treatments (proppant volume, fracture spacing, and sequencing) to maximize reservoir drainage and to increase EURs. This should lead to more-effective completion designs.